CONTROL OF RED MITE AND BLACK-SPOT.

New Zealand Journal of Agriculture, Volume XVIII, Issue 6, 20 June 1919, Page 344

CONTROL OF RED MITE AND BLACK-SPOT.

SPECIAL CLUSTER-BUD SPRAYING.

By

T. E. RODDA,

Manager of the Arataki Horticultural Station.

Further series of experiments were conducted at the Arataki Horticultural Station during the past season to ascertain the value of oil and lime-sulphur sprays for the control, of red mite on apple-trees, when applied at reduced strengths late in the season, commencing from the period of pronounced bud-movement up to the time that the buds were in the advanced-pink stage. Bordeaux was also applied prior to the oil as a check against lime-sulphur for the control of black-spot.

The bordeaux was in each instance - followed. the same day by oil. The main purpose of this was to ascertain whether bordeaux was by this means made more efficacious and lasting in its effects, and at the same time to ascertain how late the combined spray could be applied with safety. Lime-sulphur. was used on the sister trees at the same strength as the oil. Particulars are indicated in ’ the following outline

of the experiments

There would be about twenty-eight days’ difference between the applications on plots i and 4, with a difference between each plot of eight to ten days. On plots 1. and 2 no summer insecticide was used for mite. Woolly aphis was hand-painted with oil. Trees . showing signs of black-spot were sprayed with bordeaux, 3-4-50. Arsenate of lead was applied regularly.

NOTES ON THE PLOTS.

Plot 1. — An examination made on 14th November revealed a fair number of mites present. These rapidly increased as the season advanced, being especially noticeable on trees treated with lime-sulphur. At the time of a later inspection, on 23rd April, all the trees were badly

infested with winter eggs. At the first examination black-spot was showing rather pronounced on some trees treated with ' lime-sulphur, and to a much less extent on a few trees treated with Bordeaux and oil. The affected trees were then' sprayed ' with Bordeaux, 3-4-50, after the fruit was well formed. No further development of blackspot took place throughout the block. There was no spray russeting on the fruit.

Plot 2. No'live mites ■ on 14th November, and only one fruit infected with spot. Live mites developed as the season advanced. It. was very noticeable that the mites increased at a very much greater rate on the trees treated with lime-sulphur. All rows were free from spray russeting.

Plot 3. — There were very few live mites on 14th November, but they were fairly plentiful by 12th December, and towards the end of April were very numerous on all trees, more especially on the limesulphur rows. Oil, 1-30, was more effective than the weaker strengths. Black-spot development was pronounced on the lime-sulphur treatment, while it developed to a much less extent on those trees treated with Bordeaux and oil.. The fruit on the trees sprayed with the latter was very badly russeted, but was very bright and of fine appearance on all trees treated with lime-sulphur. No arsenate of lead was applied until 23rd December. No other summer insecticide was used.

Plot 4. — Live mites were showing on 14th November, and became very numerous as the season advanced. The Bordeaux and oil, 1-60, did not appear to russet the fruit quite so badly as Bordeaux and oil, 1-40 and 1-45, in plot 3. Black-spot appeared on fruit treated with lime-sulphur, but there was no sign of the disease on the rows treated with Bordeaux. Again, the fruit on those rows treated with lime-sulphur was of bright appearance. As in plot 3, no arsenate of lead was applied until 23rd December. No other summer insecticide was used. t • ■

Plot 3. — Where oil was applied without Bordeaux red-mite control was very satisfactory, but where used after the- Bordeaux, oil, 1-30, gave only slightly better results than Bordeaux and oil, 1-60, in plot 4. Black-spot developed on those trees treated with oil alone, while those that had Bordeaux in addition were clean. Bordeaux and oil, 1-30, russeted the fruit very badly, while the oil alone did almost as much injury. -

Plots 6 and, 7. —These plots were used to ascertain whether delaying the spraying for eight to ten days from one stage to the other would increase the amount of russeting. It will be noticed that the same strength was used both in the - open - cluster and advanced - pink stages. Sister trees were used for the purpose. There was an average of 55 per cent, of fruit russeted in open cluster and 70 per cent, in advanced pink.

Plot 8. — This plot was to demonstrate whether oil alone would blemish the fruit. There was similar russeting to plots 6 and 7 where Bordeaux was used in addition. ?

CONCLUSIONS.

The results derived from the past season's work confirm the previous year’s experiments. Although the oil used at the bud-move-ment and ■ tight-cluster periods did not injure the buds or retard growth, it was demonstrated that the applications were not of sufficient strength to be of any material advantage in controlling red mite. It may be that oil alone at this stage would be efficacious, but this would need to be tested. Oil, 1-30, used alone in advanced pink gave very satisfactory results. At all stages of bud-development one application of lime-sulphur at any of the strengths used was of no practical value in controlling red mite. The writer is of the opinion that the buds will stand lime-sulphur. a good deal stronger in all stages of development, and possibly something may be gained by using it at increased strengths.

In regard to black-spot control the qualities of bordeaux were outstanding, while on the other hand there can be no question that lime-sulphur produces the brightest and cleanest-skinned fruit.

. There is nothing to be gained by using bordeaux and oil on the same day, or even oil alone, when growth is beyond the tight-cluster stage. To apply oil after this.period of development is decidedly too dangerous and has nothing to recommend it. Although the bordeaux and oil controlled black-spot fairly well in the pink, it russeted the fruit to. such an extent as to render it very unsightly for market, and as a result makes this combination when applied at that stage or later of little or no practical value.

Expeditionary Force Scholarships. Among the recipients of scholarships awarded in England to members of the New Zealand Expeditionary Force is Captain W. S. Hill, B.Sc.Ag., formerly Plant-breeder in the Department of Agriculture, who will study agriculture at the Imperial College, of Science, London, and Wye Agricultural College, Kent. A scholarship has also been awarded to Sergeant W. H. Udy, of the Chemistry Section of the Department, to study agricultural science at King’s College, London. .

Farm-manure Experiment with Onions.— In the horticultural section at Ruakura Farm of Instruction during the past season an experiment was conducted on various kinds of farm manure with onions. Four plots, each 14 yards by 8 yards, were dressed in April, 1918, as follows : (1) Horse-manure, (2) fowl-manure, (3) pig-manure, (4) cow-manure—-each at the rate of 15 tons per acre. The plots were immediately dug under and left until the middle of. July, when they were lightly forked over. In the middle of August the onions (Straw-coloured Spanish) were transplanted into the plots, basic super at the rate of 2 cwt. per acre being applied in each case at the same time. The crop was harvested in the middle of February, when the following yields were recorded : Pig-manure plot, 832 lb. ; fowl-manure plot, 742 lb. ; horse-manure plot, 647 lb. ; cow-manure plot, 588 lb. The manure was from animals fed under good average New Zealand conditions.

Plot I I — Treatment. Period applied. Row i. Treatment. Bordeaux, 6-4-50, and oil, i-i5 Period applied. Just after bud-movement. ,, 2. Lime-sulphur, 1—15 . V. f*. » 3Bordeaux, 6-4—50, and oil, 1-20 y> >*- 4-Lime-sulphur, 1—20 . . ■ ' )) Plot 2 — 2 Row. 5. Bordeaux, 6-4-50, and oil, 1-25 Tight cluster. „ 6. Lime-sulphur, 1-20 . . „ 7Bordeaux, 6—4—50, and oil, 1-25 ,, „ - 8. Lime-sulphur, 1-25 . . ,, -• Plot 3 — 3— Row 9. Bordeaux, 6-4-50, and oil, 1-30 Pink. ,, ' 10. Lime-sulphur, 1—30 . . t . ■ ,, . ,, ii. Bordeaux, 6—4—50, and oil, 1-40 ' )) ,, 12. Lime-sulphur, 1-40 . . ,, „ 13Bordeaux, 6-4-50, and oil, i-45 yy " X / ,, , 14-Lime-sulphur, 1-45 . . .)) Plot 4 — 4— Row 15. Bordeaux, 6-4-50, and oil, 1-50 Advanced pink. ,, 16. Lime-sulphur, -50 . . >> 7Bordeaux, 6-4-50, and oil, 1-60 ,, „ 18. Lime-sulphur, 1-60 . . yy Plot 5— 5— Row 19. Bordeaux, 6—4—50, and oil, 1-30 , , ,, 20. Oil, 1-30 . . .. . yy Plot 6— 6— Row 21. Bordeaux, 6—4—50, and oil, 1-25 Open cluster. „ 22. „ 6-4-50, 1-25 Advanced pink. Plot 7 — 7— Row 23. „ 6-4-50, 1-30 Open cluster. „ 24. „ 6-4-50, „ 1-30 Advanced pink. Plot 8— 8— Row 25. Oil, 1-30 . . Open cluster. ,, 26. „ 1-30 .. Advanced pink.